At 2.5 feet (0.7 meters) long, the newfound dino is the smallest Alvarezsaur ever found in North America, Longrich said.

Proportionally, its arms were as short or shorter than T. rex's, but much more powerfully built.

"They look like the forelimbs of a mole," Longrich told National Geographic News.

But unlike moles, Albertonykus's arms would not have been useful for digging. Its hand had only two stunted fingers and a massive picklike thumb.

The team speculates that Albertonykus dined on insects, and that it used its large thumb claw to tear open rotten logs packed with termites and other critters.

Skull fragments of other Alvarezsaurs found in Asia suggest Albertonykus had a long snout filled with tiny teeth similar to those of certain insect-eating mammals alive today, such as armadillos and some species of anteaters, Longrich said.

He and colleagues describe the dinosaur in the current issue of the journal Cretaceous Research.

Ancient Migrations

Hans-Dieter Sues is a paleontologist at the Smithsonian National Museum of Natural History in Washington, D.C., who was not involved in the study.

Sues said the new discovery underscores the movement of Alvarezsaurs and other different dinosaur groups between East Asia and North and South America.

"It's a North American record of these creatures, which we previously had only a few isolated bones of," he said.

As for Albertonykus's small size, it's possible the specimens the researchers analyzed had not yet reached adulthood, Sues said.

"The key thing to determining whether a dinosaur is a youngster or a really tiny adult is to see vertebrae, because the different parts only fuse at maturity," he said.

"In this case, it may simply be that they are small individuals that are not fully grown yet."